Polyolefin compositions for photovoltaic encapsulant films

ABSTRACT

This disclosed is an encapsulant film made from a curable composition comprising: (A) a polyolefin polymer; (B) an organic peroxide; (C) a silane coupling agent; and (D) a co-agent comprising a silane compound of formula (I). This further disclosed is a process for preparing said encapsulant film.

FIELD OF THE DISCLOSURE

This disclosure relates to polyolefin polymer compositions forphotovoltaic (PV) encapsulant films. In one aspect, the disclosurerelates to polyolefin polymer compositions that provide for shorterprocess times for forming encapsulant films. In another aspect, thedisclosure relates to PV encapsulant films comprising a polyolefinpolymer composition and electronic devices including the same.

BACKGROUND

The global demand for alternative energy has resulted in large increasesin solar panel and PV module production over the last decade. The solarcells (also called PV cells) that convert solar energy into electricalenergy are extremely fragile and must be surrounded by a durableencapsulant film. Two main functions of the encapsulant film are to (1)bond the solar cell to the glass coversheet and the backsheet and (2)protect the PV module from environmental stress (e.g., moisture,temperature, shock, vibration, electrical isolation, etc.). Currentencapsulant films are primarily made of ethylene vinyl acetate (EVA)because EVA shows a good balance of properties necessary for encapsulantfilms. EVA is a type of ethylene/unsaturated carboxylic ester copolymerin which the unsaturated carboxylic ester comonomer is a vinylcarboxylate.

Certain polyolefin polymers, such as polyolefin elastomers (POE) thatare not ethylene/unsaturated carboxylic ester copolymers, have beenidentified as an alternative to EVA for forming encapsulant films andhave, in comparison to EVA, advantages in, e.g., electric resistivity,wet and heat stability, and weather resistance. However, conventionalPOE-based compositions have longer process times for forming encapsulantfilms compared to EVA-based compositions. Consequently, the artrecognizes a need for novel POE-based compositions that provide forshort process times for forming encapsulant films while maintaining goodperformance for curing, adhesion, volume resistivity, etc.

SUMMARY

In certain embodiments, this disclosure is directed to a curablecomposition for forming an encapsulant film, the composition comprising:

-   -   (a) a polyolefin polymer;    -   (b) an organic peroxide;    -   (c) a silane coupling agent; and    -   (d) a co-agent comprising a silane compound of formula (I):

wherein subscript n is an integer from 0 to 2; each R1 is independentlya (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et; and each R2 isindependently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et,or R1.

In further embodiments, this disclosure is directed to an encapsulantfilm comprising a crosslinked polymeric composition comprising thereaction product of:

(a) a polyolefin polymer;

(b) an organic peroxide;

(c) a silane coupling agent; and

(d) a co-agent comprising a silane compound of formula (I):

-   -   wherein subscript n is an integer from 0 to 2; each R1 is        independently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me,        O-Et; and each R2 is independently a (C₂-C₄)alkenyl, H, a        (C₁-C₆)alkyl, phenyl, O-Me, O-Et, or R1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an exemplary photovoltaicmodule.

FIG. 2 is a soaking time versus soaking percentage curve for certainexamples of this disclosure.

DEFINITIONS

Any reference to the Periodic Table of Elements is that as published byCRC Press, Inc., 1990-1991. Reference to a group of elements in thistable is by the new notation for numbering groups.

For purposes of United States patent practice, the contents of anyreferenced patent, patent application or publication are incorporated byreference in their entirety (or its equivalent US version is soincorporated by reference) especially with respect to the disclosure ofdefinitions (to the extent not inconsistent with any definitionsspecifically provided in this disclosure) and general knowledge in theart.

The numerical ranges disclosed herein include all values from, andincluding, the lower and upper value. For ranges containing explicitvalues (e.g., 1, or 2, or 3 to 5, or 6, or 7), any subrange between anytwo explicit values is included (e.g., 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5to 6; etc.).

Unless stated to the contrary, implicit from the context, or customaryin the art, all parts and percents are based on weight and all testmethods are current as of the filing date of this disclosure.

Unless stated to the contrary, all test methods are current as of thefiling date of this disclosure.

“Blend”, “polymer blend” and like terms mean a composition of two ormore polymers. Such a blend may or may not be miscible. Such a blend mayor may not be phase separated. Such a blend may or may not contain oneor more domain configurations, as determined from transmission electronspectroscopy, light scattering, x-ray scattering, and any other methodused to measure and/or identify domain configurations. Blends are notlaminates, but one or more layers of a laminate may contain a blend.

“Composition,” as used herein, includes a mixture of materials whichcomprise the composition, as well as reaction products and decompositionproducts formed from the materials of the composition.

The terms “comprising,” “including,” “having,” and their derivatives,are not intended to exclude the presence of any additional component,step or procedure, whether or not the same is specifically disclosed. Inorder to avoid any doubt, all compositions claimed through use of theterm “comprising” may include any additional additive, adjuvant, orcompound, whether polymeric or otherwise, unless stated to the contrary.In contrast, the term, “consisting essentially of” excludes from thescope of any succeeding recitation any other component, step orprocedure, excepting those that are not essential to operability. Theterm “consisting of” excludes any component, step or procedure notspecifically listed. The term “or,” unless stated otherwise, refers tothe listed members individual as well as in any combination. Use of thesingular includes use of the plural and vice versa.

“Directly contacts” refers to a layer configuration whereby a firstlayer is located immediately adjacent to a second layer and nointervening layers or no intervening structures are present between thefirst layer and the second layer.

The term “coagent” means a compound that enhances crosslinking, i.e., acuring coagent. The term “coagent,” “co-agent,” “crosslinking coagent,”and “crosslinking co-agent” are used interchangeably herein.“Conventional coagent” is an acyclic or cyclic compound that enhancescrosslinking and contains carbon atoms in its respective backbone orring substructure. Thus, the backbone or ring substructure of theconventional coagent is based on carbon (carbon-based substructure). Incontrast, a silicon-based coagent means an acyclic or cyclic compoundthat enhances crosslinking and that contains silicon atoms in itsrespective backbone or ring substructure. The silane compound of formula(I) is an acyclic silicon-based coagent. Use of a conventional coagentin a POE-based composition is representative of the state of the art.

The terms “curing” and “crosslinking” are used interchangeably herein tomean forming a crosslinked product (network polymer).

“Polymer,” as used herein, refers to a polymeric compound prepared bypolymerizing monomers, whether of the same or a different type. Thegeneric term polymer thus embraces the term homopolymer (employed torefer to polymers prepared from only one type of monomer, with theunderstanding that trace amounts of impurities can be incorporated intothe polymer structure), and the term interpolymer as defined herein.Trace amounts of impurities, for example, catalyst residues, may beincorporated into and/or within the polymer.

“Interpolymer,” as used herein, refers to polymers prepared by thepolymerization of at least two different types of monomers. The genericterm interpolymer thus includes copolymers (employed to refer topolymers prepared from two different types of monomers), and polymersprepared from more than two different types of monomers.

“Propylene-based,” “a propylene-based polymer,” “polypropylene,” andlike terms refer to a polymer that contains 50 weight percent (wt %) to100 wt % of polymerized propylene monomers (based on the total amount ofpolymerizable monomers) and, optionally, may contain at least onecomonomer. Such terms include propylene homopolymers and propyleneinterpolymers (meaning units derived from propylene and one or morecomonomers, such as propylene/alpha-olefin interpolymers).

“Ethylene-based,” “an ethylene-based polymer,” “polyethylene,” and liketerms refer to a polymer that contains 50 wt % to 100 wt % ofpolymerized ethylene monomers (based on the total amount ofpolymerizable monomers) and, optionally, may contain at least onecomonomer. Such terms include ethylene homopolymers and ethyleneinterpolymers (meaning units derived from ethylene and one or morecomonomers, such as ethylene/alpha-olefin interpolymers).

“Alpha-olefins” as used herein are hydrocarbon molecules having anethylenic unsaturation at the primary (alpha) position. For example,“(C₃-C₂₀)alpha-olefins,” as used herein, are hydrocarbon moleculescomposed of hydrocarbon molecules comprising (i) only one ethylenicunsaturation, this unsaturation located between the first and secondcarbon atoms, and (ii) at least 3 carbon atoms, or of 3 to 20 carbonatoms. For example, (C₃-C₂₀) alpha-olefin, as used herein, refers toH₂C═C(H)—R, wherein R is a straight chain (C₁-C₁₈)alkyl group.(C₁-C₁₈)alkyl group is a monovalent unsubstituted saturated hydrocarbonhaving from 1 to 18 carbon atoms. Non-limiting examples of R are methyl,ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, and octadecyl. Non-limiting examples of the (C₃-C₂₀)alpha-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene,1-dodecene, and mixtures of two or more of these monomers. The (C₃-C₂₀)alpha-olefin may have a cyclic structure such as cyclohexane orcyclopentane, resulting in an alpha-olefin such as3-cyclohexyl-1-propene (allyl cyclohexane) and vinyl cyclohexane. The(C₃-C₂₀) alpha-olefin may be used as a comonomer with ethylene monomer.

“Polyolefin elastomer” or “POE” refer to an elastomeric polymercontaining equal to or greater than 50 wt % of polymerized alpha-olefinmonomers (including ethylene). “Polyolefin elastomer” include but arenot limited to the ethylene-based polymers and propylene-based polymersdescribed herein. As used herein, the term “polyolefin elastomer”excludes ethylene-vinyl acetate (EVA) copolymers.

“Non-polar polymer” and like terms refer to a polymer that does not havea permanent dipole, i.e., the polymer does not have a positive end and anegative end, and is void of heteroatoms and functional groups.“Functional group” and like terms refer to a moiety or group of atomsresponsible for giving a particular compound its characteristicreactions. Non-limiting examples of functional groups includeheteroatom-containing moieties, oxygen-containing moieties (e.g.,alcohol, aldehyde, ester, ether, ketone, and peroxide groups), andnitrogen-containing moieties (e.g., amide, amine, azo, imide, imine,nitratie, nitrile, and nitrite groups). A “heteroatom” is an atom otherthan carbon or hydrogen.

“Photovoltaic cell”, “PV cell” and like terms mean a structure thatcontains one or more photovoltaic effect materials of any of severalinorganic or organic types which are known in the art. For example,commonly used photovoltaic effect materials include one or more of theknown photovoltaic effect materials including but not limited tocrystalline silicon, polycrystalline silicon, amorphous silicon, copperindium gallium (di)selenide (CIGS), copper indium selenide (CIS),cadmium telluride, gallium arsenide, dye-sensitized materials, andorganic solar cell materials. As shown in FIG. 1, PV cells are typicallyemployed in a laminate structure and have at least one light-reactivesurface that converts the incident light into electric current.Photovoltaic cells are well known to practitioners in this field and aregenerally packaged into photovoltaic modules that protect the cell(s)and permit their usage in their various application environments,typically in outdoor applications. PV cells may be flexible or rigid innature and include the photovoltaic effect materials and any protectivecoating surface materials that are applied in their production as wellas appropriate wiring and electronic driving circuitry.

“Photovoltaic module”, “PV module” and like terms refer to a structureincluding a PV cell. A PV module may also include a cover sheet, frontencapsulant film, rear encapsulant film and backsheet, with the PV cellsandwiched between the front encapsulant film and rear encapsulant film.

“Room temperature” refers to a temperature range of about 20 to about25° C.

“Further processing,” “further processed,” and like terms refer tomanufacturing process steps for polyolefins, including but not limitedto compounding, blending, melt blending, extrusion (e.g., filmextrusion), kneading, imbibing, injecting, and molding (e.g., injectionmolding, compression molding, blow molding, etc.). Non-limiting examplesof suitable compounding equipment include internal batch mixers (e.g.,BANBURY and BOLLING internal mixer) and continuous single or twin screwmixers (e.g., FARREL continuous mixer, BRABENDER single screw mixer,WERNER and PFLEIDERER twin screw mixers and BUSS kneading continuousextruder). The type of mixer utilized, and the operating conditions ofthe mixer, can affect properties of the composition such as viscosity,volume resistivity, and extruded surface smoothness.

DETAILED DESCRIPTION

Currently, encapsulant films are primarily made of EVA. However, thereis strong interest in replacing EVA-based compositions with polyolefinpolymer compositions that do not include EVA (e.g., polyolefinelastomers (POE) defined herein) due to certain advantages they canprovide for encapsulant films (including but not limited to electricresistivity, wet and heat stability, and weather resistance). However, achallenge that exists for forming POE-based encapsulant films is thelonger process time relative to the formation of EVA-based encapsulantfilms. Specifically, in the process for forming an EVA-based orPOE-based encapsulant film, an initial step may be to soak the EVA orPOE with a curing package (including a peroxide, a silane couplingagent, and a crosslinking co-agent). For POE, this initial soaking stepcan be much longer (e.g., up to 16 hours) compared to EVA (e.g., around1 hour) when a conventional curing package is used. Accordingly, thelonger soaking time for POE can severely limit productivity and increasemanufacturing costs for forming POE-based encapsulant films. To thatend, this disclosure provides for a surprising and unexpected shorteningof the time required for soaking POE with a curing package whenconventional crosslinking co-agents (e.g., triallyl isocyanurate (TAIC))are replaced with co-agents comprising silane compounds of formula (I).

Composition

The composition of this disclosure (“the present composition”) is acurable composition for forming encapsulant films, the compositioncomprising: (A) a polyolefin polymer; (B) an organic peroxide; (C) asilane coupling agent; and (D) a co-agent comprising a silane compoundof formula (I).

(A) Polyolefin Polymer

The present composition comprises a polyolefin polymer. In certainembodiments, the present composition comprises from 80 wt % to 99.99 wt% (e.g., from 80 wt % to 99.88 wt %, from 85 wt % to 99.88 wt %, from 88wt % to 99.88 wt %, from 90 wt % to 99.88 wt %, from 90 wt % to 99 wt %,from 95 wt % to 99 wt %, from 97 wt % to 99 wt %, from 98 wt % to 99 wt%, from 98 wt % to 98.75 wt %, from 98 wt % to 98.75 wt %, and/or from98.25 wt % to 98.5 wt %, etc.) of the polyolefin polymer. Said inanother way, in certain embodiments, the present composition comprisesfrom 80 wt %, or 85 wt %, or 88 wt %, or 90 wt %, or 95 wt %, or 97 wt%, or 98 wt %, or 98.25 wt % to 98.5 wt %, or 98.75 wt %, or 99 wt %, or99.88 wt %, or 99.99 wt % of the polyolefin polymer.

In certain embodiments, the polyolefin polymer is a polyolefin elastomeras defined herein. In further embodiments, the polyolefin polymer is anon-polar polyolefin elastomer.

In some embodiments, the polyolefin polymer is an ethylene-based polymercomprising 50 to 100 wt % ethylenic monomeric units, 50 to 0 wt %(C₃-C₂₀) alpha-olefin-derived comonomeric units, and optionally 20 to 0wt % dienic comonomeric units, wherein the total weight percent is 100wt %. The diene used to make the dienic comonomeric units may be1,3-butadiene, 1,5-hexadiene, 1,7-octadiene, ethylidene norbornene,dicyclopentadiene, or vinyl norbornene.

In some embodiments, the polyolefin polymer is a propylene-based polymercomprising 50 to 100 wt % propylenic monomeric units, 50 to 0 wt % ofethylenic or (C₄-C₂₀) alpha-olefin-derived comonomeric units, andoptionally 20 to 0 wt % dienic comonomeric units, wherein the totalweight percent is 100 wt %. The diene used to make the dieniccomonomeric units may be 1,3-butadiene, 1,5-hexadiene, 1,7-octadiene,ethylidene norbornene, dicyclopentadiene, or vinyl norbornene.

In some embodiments, the polyolefin polymer is apoly((C₃-C₂₀)alpha-olefin) homopolymer containing 99 to 100 wt %(C₃-C₂₀)alpha-olefin monomeric units or a poly((C₃-C₂₀)alphaolefin)copolymer containing 99 to 100 wt % of at least two different(C₃-C₂₀)alpha-olefin monomeric/comonomeric units.

In certain embodiments, the polyolefin polymer is free of (i.e., lacks)heteroatoms. As defined herein, a heteroatom is an atom different fromcarbon or hydrogen (i.e., nitrogen, oxygen, sulfur, and the halogens).

In certain embodiments, the polyolefin polymer is anethylene/alpha-olefin interpolymer. Ethylene/alpha-olefin interpolymerscan be random or block interpolymers. Block interpolymers includemulti-block copolymers and di-block copolymers. Non-limiting examples ofsuitable ethylene/alpha-olefin interpolymers include ethylene/propylene,ethylene/butene, ethylene/1-hexene, ethylene/1-octene,ethylene/propylene/1-octene, ethylene/propylene/1-butene, andethylene/butene/1-octene interpolymers. In some embodiments, theethylene/alpha-olefin interpolymer is an ethylene/alpha-olefincopolymer. Non-limiting examples of suitable ethylene/alpha-olefincopolymers include ethylene/propylene copolymers, ethylene/butenecopolymers, ethylene/1-hexene copolymers, and ethylene/1-octenecopolymers.

In certain embodiments, the polyolefin polymer is apropylene/alpha-olefin interpolymer, where “alpha-olefin” includesethylene. In some embodiments, the propylene/alpha-olefin interpolymeris a propylene/alpha-olefin copolymer.

In certain embodiments, the polyolefin polymer has a density from 0.850g/cc to 0.900 g/cc (e.g., from 0.855 g/cc to 0.900 g/cc, from 0.860 g/ccto 0.900 g/cc, from 0.865 g/cc to 0.900 g/cc, from 0.870 g/cc to 0.890g/cc, from 0.875 g/cc to 0.890 g/cc, from 0.875 g/cc to 0.885 g/cc,and/or from 0.880 g/cc to 0.885 g/cc) according to ASTM D792. Said inanother way, the polyolefin polymer has a density from 0.850 g/cc, or0.855 g/cc, or 0.860 g/cc, or 0.865 g/cc, or 0.870 g/cc, or 0.875 g/cc,or 0.880 g/cc to 0.885 g/cc, or 0.890 g/cc, or 0.900 g/cc according toASTM D792.

In certain embodiments, the polyolefin polymer has a melt index (MI)from 1 g/10 min to 100 g/10 min (e.g., from 1 g/10 min to 75 g/10 min,from 1 g/10 min to 50 g/10 min, 1 g/10 min to 45 g/10 min, from 1 g/10min to 40 g/10 min, from 1 g/10 min to 35 g/10 min, from 1 g/10 min to30 g/10 min, from 5 g/10 min to 25 g/10 min, from 10 g/10 min to 25 g/10min, from 15 g/10 min to 25 g/10 min, from 15 g/10 min to 20 g/10 min,and/or from 18 g/10 min to 20 g/10 min) according to ASTM D1238, at 190°C./2.16 kg. Said in another way, in certain embodiments, the polyolefinpolymer has a melt index from 1 g/10 min, or 5 g/10 min, or 10 g/10 min,or 15 g/10 min, or 18 g/10 min to 20 g/10 min, or 25 g/10 min, or 30g/10 min, or 35 g/10 min, or 40 g/10 min, or 45 g/10 min, or 50 g/10min, or 75 g/10 min, or 100 g/10 min according to ASTM D1238, at 190°C./2.16 kg.

In some embodiments, the polyolefin polymer has a melting point from 40°C. to 125° C. In some embodiments, the polyolefin polymer has a meltingpoint from 40° C., or 45° C., or 50° C., or 55° C. to 60° C., or 65° C.,or 70° C., or 80° C., or 90° C., or 95° C., or 100° C., or 110° C., or120° C., or 125° C.

In some embodiments, the polyolefin polymer has a glass transitiontemperature (Tg) from −35° C. to −100° C. In some embodiments, the glasstransition temperature (Tg) of the polyolefin polymer is from −35° C.,or −40° C., or −45° C. or −50° C. to −80° C., or −85° C., or −90° C., or−95° C., or −100° C.

In certain embodiments, the polyolefin polymer is anethylene/alpha-olefin interpolymer having one, some, or all of thefollowing properties:

-   -   (i) a density of 0.850 g/cc, or 0.855 g/cc, or 0.860 g/cc, or        0.865 g/cc, or 0.870 g/cc, or 0.875 g/cc, or 0.880 g/cc to 0.885        g/cc, or 0.890 g/cc, or 0.900 g/cc;    -   (ii) a melt index of 1 g/10 min, or 5 g/10 min, or 10 g/10 min,        or 15 g/10 min, or 18 g/10 min to 20 g/10 min, or 25 g/10 min,        or 30 g/10 min, or 35 g/10 min, or 40 g/10 min, or 45 g/10 min,        or 50 g/10 min, or 75 g/10 min, or 100 g/10 min; and/or    -   (iii) a melting point (Tm) of 40° C., or 45° C., or 50° C., or        55° C. to 60° C., or 65° C., or 70° C., or 80° C., or 90° C., or        95° C., or 100° C., or 110° C., or 120° C., or 125° C.

The polyolefin polymer may be a blend or combination of two or more ofthe foregoing embodiments. The polyolefin polymer may also be blended ordiluted with one or more other polymers.

The polyolefin polymer may be made by any suitable process known in theart. Any conventional or hereafter discovered production process forproducing polyolefin polymers may be employed for preparing thepolyolefin polymer of this disclosure. Suitable production processescomprise one or more polymerization reactions, such as high pressurepolymerization processes or coordination polymerization processesconducted using one or more polymerization catalysts, including but notlimited to Ziegler-Natta, chromium oxide, metallocene, constrainedgeometry, or postmetallocene catalysts. Suitable temperatures are from0° to 250° C., or 30° or 200° C. Suitable pressures are from atmosphericpressure (101 kPa) to 10,000 atmospheres (approximately 1,013MegaPascals (“MPa”)). In most polymerization reactions, the molar ratioof catalyst to polymerizable olefins (monomer/comonomer) employed isfrom 10⁻¹²:1 to 10⁻¹:1, or from 10⁻⁹:1 to 10⁻⁵:1.

Non-limiting examples of the polyolefin polymer include ENGAGE™Polyolefin Elastomers from The Dow Chemical Company, AFFINITY™Polyolefin Plastomers from The Dow Chemical Company, INFUSE™ OlefinBlock Copolymers from The Dow Chemical Company, INTUNE™ PP-based OlefinBlock Copolymers from The Dow Chemical Company, EXACT™ resins from ExxonChemical Company, TAFMER™ resins from Mitsui Chemicals, LUCENE™ resinsfrom LG Chemical, EASTOFLEX™ resins from Eastman Chemical Company, andFLEXOMER™ resins from The Dow Chemical Company.

(B) Organic Peroxide

The present composition comprises an organic peroxide. In certainembodiments, the present composition comprises from 0.1 wt % to 5 wt %(e.g., from 0.1 wt % to 3 wt %, from 0.5 wt % to 2 wt %, from 0.5 wt %to 1.5 wt %, and/or from 1 wt % to 1.5 wt %) of an organic peroxide.Said in another way, the present composition comprises from 0.1 wt %, or0.5 wt %, or 1 wt % to 1.5 wt %, or 2 wt %, or 3 wt %, or 5 wt % of anorganic peroxide.

In certain embodiments, the organic peroxide is a molecule containingcarbon atoms, hydrogen atoms, and two or more oxygen atoms, and havingat least one —O—O— group, with the proviso that when there are more thanone —O—O— groups, each —O—O— group is bonded indirectly to another —O—O—group via one or more carbon atoms, or collection of such molecules.

The organic peroxide may be a monoperoxide of formula R^(O)—O—O—R^(O),wherein each R^(O) independently is a (C₁-C₂₀)alkyl group or(C₆-C₂₀)aryl group. Each (C₁-C₂₀)alkyl group independently isunsubstituted or substituted with 1 or 2 (C₆-C₁₂)aryl groups. Each(C₆-C₂₀)aryl group is unsubstituted or substituted with 1 to 4(C₁-C₁₀)alkyl groups. Alternatively, the organic peroxide may be adiperoxide of formula R^(O)—O—O—R—O—O—R^(O), wherein R is a divalenthydrocarbon group such as a (C₂-C₁₀)alkylene, (C₃-C₁₀)cycloalkylene, orphenylene, and each R^(O) is as defined above.

Non-limiting examples of suitable organic peroxides include dicumylperoxide; lauryl peroxide; benzoyl peroxide; tertiary butyl perbenzoate;di(tertiary-butyl) peroxide; cumene hydroperoxide;2,5-dimethyl-2,5-di(t-butyl-peroxy)hexyne-3;2,-5-di-methyl-2,5-di(t-butyl-peroxy)hexane; tertiary butylhydroperoxide; isopropyl percarbonate;alpha,alpha′-bis(tertiary-butylperoxy)diisopropylbenzene;t-butylperoxy-2-ethylhexyl-monocarbonate;1,1-bis(t-butylperoxy)-3,5,5-trimethyl cyclohexane;2,5-dimethyl-2,5-dihydroxyperoxide; t-butylcumylperoxide;alpha,alpha′-bis(t-butylperoxy)-p-diisopropyl benzene;bis(1,1-dimethylethyl) peroxide; bis(1,1-dimethylpropyl) peroxide;2,5-dimethyl-2,5-bis(1,1-dimethylethylperoxy) hexane;2,5-dimethyl-2,5-bis(1,1-dimethylethylperoxy) hexyne;4,4-bis(1,1-dimethylethylperoxy) valeric acid; butyl ester;1,1-bis(1,1-dimethylethylperoxy)-3,3,5-trimethylcyclohexane; benzoylperoxide; tert-butyl peroxybenzoate; di-tert-amyl peroxide (“DTAP”);bis(alpha-t-butyl-peroxyisopropyl) benzene (“BIPB”); isopropylcumylt-butyl peroxide; t-butylcumylperoxide; di-t-butyl peroxide;2,5-bis(tbutylperoxy)-2,5-dimethylhexane;2,5-bis(t-butylperoxy)-2,5-dimethylhexyne-3,1,1-bis(tbutylperoxy)-3,3,5-trimethylcyclohexane;isopropylcumyl cumylperoxide; butyl 4,4-di(tertbutylperoxy) valerate;di(isopropylcumyl) peroxide; and the like.

Non-limiting examples of suitable commercially available organicperoxides include TRIGONOX® from AkzoNobel and LUPEROX® from ARKEMA.

(C) Silane Coupling Agent

The present composition comprises a silane coupling agent. In certainembodiments, the present composition comprises from 0.01 wt % to 2 wt %(e.g., from 0.05 wt % to 1.5 wt %, from 0.05 wt % to 1 wt %, from 0.1 wt% to 0.5 wt %, from 0.2 wt % to 0.4 wt %, from 0.2 wt % to 0.3 wt %,and/or from 0.25 wt % to 0.3 wt %) of a silane coupling agent. Said inanother way, the present composition comprises from 0.01 wt %, or 0.05wt %, or 0.1 wt %, 0.2 wt %, or 0.25 wt % to 0.3 wt %, or 0.4 wt %, or0.5 wt %, or 1 wt %, or 1.5 wt %, or 2 wt % of a silane coupling agent.

In some embodiments, the silane coupling agent contains at least onealkoxy group. Non-limiting examples of suitable silane coupling agentsinclude γ-chloropropyl trimethoxysilane, vinyl trimethoxysilane, vinyltriethoxysilane, vinyl-tris-(β-methoxy)silane, allyltrimethoxysilane,γ-methacryloxypropyl trimethoxysilane, β-(3,4-ethoxy-cyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyl trimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-aminopropyl trimethoxysilane,N-β-(aminoethyl)-γ-aminopropyl trimethoxysilane, and3-(trimethoxysilyl)propylmethacrylate.

In some embodiments, the silane coupling agent is vinyl trimethoxysilaneor 3-(trimethoxysilyl)propylmethacrylate or allyltrimethoxysilane.

(D) Co-Agent

The present composition comprises a co-agent comprising a silanecompound of formula (I):

wherein subscript n is an integer from 0 to 2; each R1 is independentlya (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et; and each R2 isindependently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et,or R1.

In certain embodiments, the co-agent of the present composition iscomposed only of the silane compound of formula (I).

In further embodiments, the silane compound of formula (I) is selectedfrom the group consisting of tetravinylsilane; trivinylmethylsilane;trivinylmethoxysilane; trivinylethoxysilane; tetraallylsilane;triallylmethylsilane; and combinations thereof.

The amount of the silane compound of formula (I) in the presentcomposition may be a crosslinking effective amount. The term“crosslinking effective amount” means a quantity (e.g., wt %) that issufficient under the circumstances to enable crosslinking polyolefinmacromolecules via multivalent crosslinker groups derived from thesilane compound of formula (I). The circumstances may include loadinglevel (wt %) of the silane compound of formula (I), loading level (wt %)of the organic peroxide in peroxide curing embodiments, or theirradiation dosage in irradiation curing embodiments. A crosslinkingeffective amount of the silane compound of formula (I) gives a greaterextent of crosslinking, at a particular loading level (wt %) of anorganic peroxide or at a particular dosage level of irradiation, than acomparative composition that is free of the silane compound of formula(I). The circumstances may also depend on the total amount, if any, ofother components or any optional additive present in the presentcomposition.

Regarding determining the crosslinking effective amount of the co-agentof the present composition, the presence of crosslinking may be detectedby an increase in torque using a moving die rheometer (MDR). In someaspects, the presence of crosslinking may be detected as a percentagesolvent extraction (Ext %). Ext %=W1/Wo*100%, wherein W1 is the weightafter extraction, Wo is original weight before extraction, / indicatesdivision, and * indicates multiplication. The absence of, or a reducedlevel of, the carbon-carbon double bond of the unsaturatedorganogroup(s) of the silane compound of formula (I) in the crosslinkedpolyolefin product (due to a coupling with the (A) polyolefin polymer)may be detected by carbon-13 or silicon-29 nuclear magnetic resonance(13C-NMR spectroscopy and/or 29Si-NMR) spectroscopy.

In certain embodiments, the composition of this disclosure comprisesfrom 0.01 wt % to 5 wt % (e.g., from 0.05 wt % to 4.5 wt %, from 0.1 wt% to 4 wt %, from 0.1 wt % to 3.5 wt %, from 0.1 wt % to 3 wt %, from0.15 wt % to 2.5 wt %, from 0.2 wt % to 2 wt %, from 0.25 wt % to 1.5 wt%, from 0.25 wt % to 1 wt %, from 0.25 wt % to 1 wt %, from 0.5 wt % to1 wt %, etc.) of the co-agent comprising the silane compound of formula(I). Said in another way, the composition of this disclosure comprisesfrom 0.01 wt %, or 0.05 wt %, or 0.1 wt %, or 0.15 wt %, or 0.2 wt %, or0.25 wt %, or 0.5 wt % to 1 wt %, or 1.25 wt %, or 1.5 wt %, or 2 wt %,or 2.5 wt %, or 3 wt %, or 3.5 wt %, or 4 wt %, or 4.5 wt %, or 5 wt %of the co-agent comprising the silane compound of formula (I).

(E) Optional Additives

In an embodiment, the present composition includes one or more optionaladditives. Non-limiting examples of suitable additives includeantioxidants, anti-blocking agents, stabilizing agents, colorants,ultra-violet (UV) absorbers or stabilizers, flame retardants,compatibilizers, fillers, hindered amine stabilizers, tree retardants,methyl radical scavengers, scorch retardants, nucleating agents, carbonblack, and processing aids.

The optional additives are present in an amount of from greater thanzero, or 0.01 wt %, or 0.1 wt % to 1 wt %, or 2 wt %, or 3 wt %, or 5 wt% based on the total weight of the present composition.

Encapsulant Films

In certain embodiments, this disclosure relates to an encapsulant filmcomprising a curable composition comprising: (A) a polyolefin polymer,(B) an organic peroxide, (C) a silane coupling agent, and (D) a co-agentcomprising a silane compound of formula (I). In some embodiments, thecurable composition forms the entirety of the encapsulant film.

In certain embodiments, this disclosure relates to an encapsulant filmcomprising a crosslinked polymeric composition comprising the reactionproduct of: (A) a polyolefin polymer, (B) an organic peroxide, (C) asilane coupling agent, and (D) a co-agent comprising a silane compoundof formula (I). In some embodiments, the crosslinked polymericcomposition forms the entirety of the encapsulant film.

In certain embodiments, this disclosure relates to a process for formingan encapsulant film comprising a curable composition or a crosslinkedpolymeric composition. In certain embodiments, the polyolefin polymer,the organic peroxide, the silane coupling agent, the co-agent comprisingthe silane compound of formula (I), and any optional additives can beadded to or combined with each other in any order or simultaneously andvia any method known in the art (e.g., soaking, compounding etc.). Insome embodiments, the organic peroxide, the silane coupling agent, theco-agent comprising the silane compound of formula (I), and any optionaladditives are combined to form a pre-mix, and the pre-mix is then addedto the polyolefin polymer before or during further processing (e.g.,compounding, extrusion, molding, etc.) via any method known in the art.In some embodiments, dry pellets of the polyolefin polymer are soakedwith the pre-mix (i.e., curing package composed of the organic peroxide,the silane coupling agent, the co-agent comprising the silane compoundof formula (I), and any optional additives) and the soaked pellets arethen further processed (e.g., compounded, extruded, molded, etc.). Incertain embodiments, the encapsulant films of this disclosure are formedby film extrusion or compression molding.

In some embodiments, this disclosure relates to a process for forming anencapsulant film, the process comprising (a) soaking a polyolefinpolymer with a pre-mix to form a soaked polyolefin polymer, wherein thepremix comprises an organic peroxide, a silane coupling agent, and aco-agent comprising the silane compound of formula (I). In furtherembodiments, step (a) is performed at a temperature of from 0° C. to100° C. (e.g., from 5° C. to 75° C., from 10° C. to 50° C., from 15° C.to 45° C., from 20° C. to 40° C., etc.). In further embodiments, step(a) is performed for a duration (i.e., a soaking time) of from 0 min to250 min (e.g., from 0 min to 225 min, from 25 min to 200 min, from 50min to 175 min, from 75 min to 150 min, from 80 min to 125 min, from 80min to 110 min, etc.).

Dry pellets of a polyolefin polymer that are soaked with a curingpackage comprising a conventional co-agent (e.g., triallyl isocyanurate(TAIC)) require a lengthy soaking time (up to 16 hours) for completesoaking of the pellets, thereby resulting in limited productivity andincreased manufacturing costs. “Complete soaking” as defined hereinrefers to a soaking percentage of from greater than 90% to 100% (e.g.,greater than or equal to 93%, greater than or equal to 95%, greater thanor equal to 97%, greater than or equal to 98%, etc.). “Soakingpercentage,” as defined herein, refers to the following:(X3−X2)/X1*100%, where X1 is the total weight of the pre-mix (composedof the organic peroxide, the silane coupling agent, and the co-agentcomprising the silane compound of formula (I)), X2 is the weight of thedry pellets of the polyolefin polymer prior to soaking step (a), X3 isthe weight of the pellets of the polyolefin polymer after soaking step(a) for a certain soaking time, / indicates division, and * indicatesmultiplication.

Surprisingly, the soaking time required for complete soaking of thepolyolefin polymer is significantly reduced when a conventional co-agentis replaced with a co-agent comprising the silane compound of formula(I). For example, in some embodiments, a soaking percentage of greaterthan 90% may be achieved when step (a) of the process is performed for aduration of less than 95 minutes at room temperature. In furtherembodiments, a soaking percentage of greater than 95% may be achievedwhen step (a) of the process is performed for a duration of less than110 minutes at room temperature. In further embodiments, a soakingpercentage of greater than or equal to 97% may be achieved when step (a)of the process is performed for a duration of less than 125 minutes atroom temperature. In further embodiments, a soaking percentage ofgreater than or equal to 98% may be achieved when step (a) of theprocess is performed for a duration of less than 90 minutes at roomtemperature. In further embodiments, a soaking percentage of 100% may beachieved when step (a) of the process is performed for a duration ofequal to or less than 110 minutes at room temperature.

Furthermore, unexpectedly, other performances required for forming anencapsulant film (e.g., curing performance, adhesion, volumeresistivity, etc.) are maintained or improved when a conventionalco-agent is replaced with a co-agent comprising the silane compound offormula (I).

In certain embodiments, the soaked pellets of the (A) polyolefin polymerare cured during further processing (e.g., compounding, extrusion,molding, etc.). Accordingly, in certain embodiments, the process forforming an encapsulant film further comprises: (2) curing and furtherprocessing the soaked polyolefin polymer to form the encapsulant film.In this regard, the temperature during further processing of the soakedpolyolefin polymer is from 80° C., or 90° C. to 100° C., or 110° C., or120° C., or 130° C., or 140° C., or 150° C., or 160° C., or 170° C.

In further embodiments, it is desirable to avoid or limit curing untilother steps, such as lamination, as discussed below. Prematurecrosslinking and/or premature decomposition of the organic peroxide mayresult in the encapsulant film having decreased glass adhesion. In otherwords, the encapsulant film comprising a curable composition remainsreactive until lamination, at which point crosslinking is completed andthe crosslinked polymeric composition of the encapsulant film becomes areaction product of the polyolefin polymer, the organic peroxide, thesilane coupling agent, and the co-agent comprising the silane compoundof formula (I). Accordingly, in further embodiments, the process forforming an encapsulant film further comprises: (2) further processingthe soaked polyolefin polymer to form a curable film. Subsequent stepsinclude but are not limited to: curing the curable film to form theencapsulant film, or curing the curable film during a lamination step toform the encapsulant film.

The temperature for further processing the soaked polyolefin polymer maytherefore be less than the decomposition temperature of the organicperoxide. In some embodiments, the temperature during further processingof the soaked polyolefin polymer is from 80° C., or 90° C. to 100° C.,or 110° C., or 120° C.

Curing as discussed herein may be free-radical curing via irradiation ofthe present composition with a curing effective dose of irradiationand/or heating the present composition at a curing effect temperaturewith an organic peroxide in such a way as to react the (A) polyolefinpolymer with the (D) co-agent comprising a silane compound of formula(I), thereby forming a crosslinked product. The combination of thecrosslinking effective amount of the co-agent comprising the silanecompound of formula (I) with the curing effective dose of irradiation orthe curing effective temperature, and any other desired reactionconditions (e.g., pressure or inert gas atmosphere) is sufficient tocure the present composition and make the crosslinked polymericcomposition of the encapsulant film. The source of irradiation may be anelectron beam, gamma radiation, ultraviolet light, or any combinationthereof.

Unpredictably, the present composition comprising a co-agent comprisingthe silane compound of formula (I) improves upon or maintains propertiesrelating to crosslinking relative to a comparative polyolefincomposition free of the silane compound of formula (I). Such propertiesinclude but are not limited to the following: the time period forachieving 90% crosslinking (“t90”) in a crosslinked polyolefin product,which indicates the curing rate; the greater maximum torque value(“MH”), which indicates the extent of crosslinking in a crosslinkedpolyolefin product; the time to scorch (“ts1”), which indicates theresistance to premature curing of a polyolefin composition duringextrusion (e.g., curing in an extruder instead of in a post-extruderoperation); and/or the ability of a co-agent to be loaded into apolyolefin composition at greater concentrations without “sweat out” ofthe co-agent during storage of the polyolefin composition over a periodof time, which indicates compatibility and/or solubility of the co-agentin the present composition.

Encapsulant Film 1:

In an embodiment, the encapsulant film is composed of a curablecomposition comprising (or a crosslinked polymeric compositioncomprising the reaction product of): (A) a polyolefin polymer, (B) anorganic peroxide, (C) a silane coupling agent, and (D) a co-agentcomprising a silane compound of formula (I).

Encapsulant Film 2:

In an embodiment, the encapsulant film is composed of a curablecomposition comprising (or a crosslinked polymeric compositioncomprising the reaction product of): (A) from 80 wt %, or 85 wt %, or 88wt %, or 90 wt %, or 95 wt %, or 97 wt %, or 98 wt %, or 98.25 wt % to98.5 wt %, or 98.75 wt %, or 99 wt %, or 99.88 wt %, or 99.99 wt % of apolyolefin polymer, (B) from 0.1 wt %, or 0.5 wt %, or 1 wt % to 1.5 wt%, or 2 wt %, or 3 wt %, or 5 wt % of an organic peroxide, (C) from 0.01wt %, or 0.05 wt %, or 0.10 wt %, 0.20 wt %, or 0.25 wt % to 0.3 wt %,or 0.4 wt %, or 0.5 wt %, or 1 wt %, or 1.5 wt %, or 2 wt % of a silanecoupling agent, (D) from 0.01 wt %, or 0.05 wt %, or 0.10 wt %, or 0.15wt %, or 0.20 wt %, or 0.25 wt %, or 0.50 wt % to 1 wt %, or 1.25 wt %,or 1.5 wt %, or 2 wt %, or 2.5 wt %, or 3 wt %, or 3.5 wt %, or 4 wt %,or 4.5 wt %, or 5 wt % of a co-agent comprising a silane compound offormula (I). It is understood that the aggregate amount of component(A), (B), (C), (D) and any optional additives yields 100 wt % of thecomposition.

Encapsulant Film 3:

In an embodiment, the encapsulant film is composed a curable compositioncomprising (or a crosslinked polymeric composition comprising thereaction product of): (A) from 95 wt % to 99 wt % of a polyolefinpolymer, (B) from 0.5 wt % to 2 wt % of an organic peroxide, (C) from0.1 wt %, to 0.5 wt % of a silane coupling agent, (D) from 0.2 wt % to 1wt % of a co-agent comprising a silane compound of formula (I). It isunderstood that the aggregate amount of component (A), (B), (C), (D) andany optional additives yields 100 wt % of the composition.

In certain embodiments, the encapsulant film is according to EncapsulantFilm 1, Encapsulant Film 2, or Encapsulant Film 3 having one, some, orall of the following properties regarding volume resistivity and glassadhesion.

In certain embodiments, the encapsulant film is according to EncapsulantFilm 1, Encapsulant Film 2, or Encapsulant Film 3 having a volumeresistivity of from 1.0*10¹⁴ ohm-cm to 1.0*10¹⁸ ohm-cm (e.g., from1.0*10¹⁵ ohm-cm to 1.0*10¹⁸ ohm-cm, from 1.0*10¹⁶ ohm-cm to 1.0*10¹⁸ohm-cm, from 1.0*10¹⁷ ohm-cm to 1.0*10¹⁸ ohm-cm, from 1.0*10¹⁷ ohm-cm to10.04′10¹⁷ ohm-cm, from 1.0*10¹⁷ ohm-cm to 5.0*10¹⁷ ohm-cm, from1.5*10¹⁷ ohm-cm to 4.5*10¹⁷ ohm-cm, from 1.8*10¹⁷ ohm-cm to 4.0*10¹⁷ohm-cm, from 1.8*10¹⁷ ohm-cm to 3.5*10¹⁷ ohm-cm, from 1.8*10¹⁷ ohm-cm to3.0*10¹⁷ ohm-cm, from 1.8*10¹⁷ ohm-cm to 2.6*10¹⁷ ohm-cm, etc.) at roomtemperature. In certain embodiments, the encapsulant film is accordingto Encapsulant Film 1, Encapsulant Film 2, or Encapsulant Film 3 havinga volume resistivity of greater than 1.0*10¹⁴ ohm-cm (e.g., greater than1.0*10¹⁵ ohm-cm, greater than 1.0*10¹⁶ ohm-cm, greater than 1.0*10¹⁷ohm-cm, greater than 1.5*10¹⁷ ohm-cm, greater than or equal to 1.8*10¹⁷ohm-cm, greater than or equal to 2.6*10¹⁷ ohm-cm, etc.) at roomtemperature.

In certain embodiments, the encapsulant film is according to EncapsulantFilm 1, Encapsulant Film 2, or Encapsulant Film 3 having a volumeresistivity of from 1.0*10¹⁴ ohm-cm to 1.0*10¹⁸ ohm-cm (e.g., from1.0*10¹⁵ ohm-cm to 1.0*10¹⁷ ohm-cm, from 1.0*10¹⁶ ohm-cm to 1.0*10¹⁷ohm-cm, from 1.0*10¹⁶ ohm-cm to 10.0*10¹⁶ ohm-cm, from 1.5*10¹⁶ ohm-cmto 9.0*10¹⁶ ohm-cm, from 2.0*10¹⁶ ohm-cm to 8.0*10¹⁶ ohm-cm, from2.0*10¹⁶ ohm-cm to 7.0*10¹⁶ ohm-cm, from 2.5*10¹⁶ ohm-cm to 6.0*10¹⁶ohm-cm, from 3.0*10¹⁶ ohm-cm to 5.0*10¹⁶ ohm-cm, from 3.5*10¹⁶ ohm-cm to4.5*10¹⁶ ohm-cm, from 3.5*10¹⁶ ohm-cm to 4.2*10¹⁶ ohm-cm, etc.) at 60°C. In certain embodiments, the encapsulant film is according toEncapsulant Film 1, Encapsulant Film 2, or Encapsulant Film 3 having avolume resistivity of greater than 1.0*10¹⁴ ohm-cm (e.g., greater than1.0*10¹⁵ ohm-cm, greater than 1.0*10¹⁶ ohm-cm, greater than or equal to2.0*10¹⁶ ohm-cm, greater than or equal to 3.0*10¹⁶ ohm-cm, greater thanor equal to 3.5*10¹⁶ ohm-cm, greater than or equal to 4.0*10¹⁶ ohm-cm,greater than or equal to 4.2*10¹⁶ ohm-cm, etc.) at 60° C.

In certain embodiments, the encapsulant film is according to EncapsulantFilm 1, Encapsulant Film 2, or Encapsulant Film 3 having an initialglass adhesion of greater than 60 N/cm (e.g., greater than 70 N/cm,greater than 80 N/cm, greater than 90 N/cm, greater than 100 N/cm,etc.).

The encapsulant film of the present disclosure may have any thickness.

In certain embodiments, the encapsulant film is one layer, wherein thesingle layer is composed of the present composition. In certainembodiments, the encapsulant film has two or more layers, wherein atleast one layer is composed of the present composition.

Electronic Devices

An encapsulant film of this disclosure is used to construct anelectronic device module. The encapsulant film is used as one or more“skins” for the electronic device, i.e., applied to one or both facesurfaces of an electronic device, e.g., as a front encapsulant film orrear encapsulant film, or as both the front encapsulant film and therear encapsulant film, e.g., in which the device is totally enclosedwithin the material.

In an embodiment, the electronic device module comprises (i) at leastone electronic device, typically a plurality of such devices arrayed ina linear or planar pattern, (ii) at least one cover sheet, and (iii) atleast one encapsulant film according to any of the embodiments disclosedherein. The encapsulant film is between the cover sheet and theelectronic device, and the encapsulant film exhibits good adhesion toboth the electronic device and the cover sheet.

In an embodiment, the electronic device module comprises (i) at leastone electronic device, typically a plurality of such devices arrayed ina linear or planar pattern, (ii) a front cover sheet, (iii) a frontencapsulant film, (iv) a rear encapsulant film, and (v) a backsheet,with at least one of the (iii) front encapsulant film and (iv) rearencapsulant film being an encapsulant film of this disclosure. Theelectronic device is sandwiched between the front encapsulant film andthe rear encapsulant film with the cover sheet and backsheet enclosingthe front encapsulant film/electronic device/rear encapsulant film unit.

In an embodiment, the cover sheet is glass, acrylic resin,polycarbonate, polyester or fluorine-containing resin. In a furtherembodiment, the cover sheet is glass.

In an embodiment, the back sheet is a single or multilayer film composedof glass, metal, or a polymeric resin. The back sheet is a film composedof glass or a polymeric resin. In a further embodiment, the back sheetis a multilayer film composed of a fluorine polymer layer and apolyethylene terephthalate layer.

In an embodiment, the electronic device is a solar cell or photovoltaic(PV) cell.

In an embodiment, the electronic device module is a PV module.

FIG. 1 illustrates an exemplary PV module. The rigid PV module 10comprises photovoltaic cell 11 (PV cell 11) surrounded or encapsulatedby the front encapsulant film 12 a and rear encapsulant film 12 b. Theglass cover sheet 13 covers a front surface of the portion of the frontencapsulant film 12 a disposed over PV cell 11. The backsheet 14, e.g.,a second glass cover sheet or polymeric substrate, supports a rearsurface of the portion of the rear encapsulant film 12 b disposed on arear surface of PV cell 11. Backsheet 14 need not be transparent if thesurface of the PV cell to which it is opposed is not reactive tosunlight. In this embodiment, the encapsulant films 12 a and 12 b fullyencapsulate PV cell 11. In the embodiment shown in FIG. 1, the frontencapsulant film 12 a directly contacts the glass cover sheet 13 and therear encapsulant film 12 b directly contacts the backsheet 14. The PVcell 11 is sandwiched between the front encapsulant film 12 a and rearencapsulant film 12 b such that the front encapsulant film 12 a and rearencapsulant film 12 b are both in direct contact with the PV cell 11.The front encapsulant film 12 a and rear encapsulant film 12 b are alsoin direct contact with each other in locations where there is no PV cell11.

An encapsulant film of this disclosure can be the front encapsulantfilm, the rear encapsulant film, or both the front encapsulant film andrear encapsulant film. In an embodiment, an encapsulant film of thisdisclosure is the front encapsulant film. In another embodiment, anencapsulant film of this disclosure is both the front encapsulant filmand the rear encapsulant film.

In an embodiment, the encapsulant film(s) of this disclosure are appliedto an electronic device by one or more lamination techniques. Throughlamination, the cover sheet is brought in direct contact with a firstfacial surface of the encapsulant film, and the electronic device isbrought in direct contact with a second facial surface of theencapsulant film. The cover sheet is brought into direct contact with afirst facial surface of the front encapsulant film, the back sheet isbrought in direct contact with a second facial surface of the rearencapsulant film, and the electronic device(s) is secured between, andin direct contact with the second facial surface of the frontencapsulant film and the first facial surface of the rear encapsulantfilm.

In an embodiment, the lamination temperature is sufficient to activatethe organic peroxide and crosslink the present composition, that is, thecurable composition comprising the polyolefin polymer, the organicperoxide, the silane coupling agent, and the co-agent comprising thesilane compound of formula (I), where the co-agent remains reactiveuntil lamination when crosslinking occurs. During crosslinking, thesilane coupling agent forms a chemical bond between two or more of themolecular chains of the polyolefin polymer by way of a silane linkage. A“silane linkage” has the structure —Si—O—Si—. Each silane linkage mayconnect two or more, or three or more, molecular chains of thepolyolefin polymer. The silane coupling agent also interacts with thesurface of the cover sheet to increase adhesion between the encapsulantfilm and the cover sheet. After lamination, the present composition is areaction product of the polyolefin polymer, the organic peroxide, thesilane coupling agent, and the co-agent comprising the silane compoundof formula (I).

In an embodiment, the lamination temperature for producing an electronicdevice is from 130° C., or 135° C., or 140° C., or 145° C. to 150° C.,or 155° C., or 160° C. In an embodiment, the lamination time is from 8minutes, or 10 minutes, or 12 minutes, or 15 minutes to 18 minutes, or20 minutes, or 22 minutes, or 25 minutes.

In an embodiment, the electronic device of this disclosure includes anencapsulant film composed of a crosslinked polymeric composition whichis the reaction product of (A) a polyolefin polymer, (B) an organicperoxide, (C) a silane coupling agent, and (D) a co-agent comprising asilane compound of formula (I), and the encapsulant film has an initialglass adhesion of greater than 60 N/cm (e.g., greater than 70 N/cm,greater than 80 N/cm, greater than 90 N/cm, greater than 100 N/cm,etc.).

In an embodiment, the electronic device of this disclosure includes anencapsulant film according to Encapsulant Film 1, Encapsulant Film 2, orEncapsulant Film 3 having one, some or all of the properties discussedbefore regarding volume resistivity and glass adhesion.

Some embodiments of this disclosure will now be described in detail inthe following examples.

EXAMPLES Test Methods

Density is measured in accordance with ASTM D792. The result is recordedin grams (g) per cubic centimeter (g/cc or g/cm³).

Glass transition temperature (Tg) is measured according to ASTM D7028.

Melt index (MI) is measured in accordance with ASTM D1238 at 190° C.,2.16 kg and reported in grams per 10 minutes (g/10 min).

Melting point is measured according to ASTM D3418.

Crosslinking or cure is tested using a moving die rheometer according toASTM D5289. The moving die rheometer (MDR) is loaded with 4 grams ofeach sample. The MDR is run for 25 minutes at 150° C., and the timeversus torque curve is provided for the samples over the given interval.The 150° C. temperature represents the module lamination temperature.The maximum torque (MH) exerted by the MDR during the 25 minute testinginterval is reported in dNm. The MH usually corresponds to the torqueexerted at 25 minutes. The time it takes for the torque to reach X % ofMH (t_(x)) is reported in minutes. t_(x) is a standardized measurementto understand the curing kinetics of each resin. The time to reach 90%of MH (T₉₀) is reported in minutes.

Glass adhesion strength (average glass adhesion strength from 1″ to 2″)is measured by the 180° peel test. Cuts are made through the backsheetand encapsulant film layers of each of the laminated samples (e.g.,comparative example and inventive example formulations) to divide eachlaminated sample into three 1-inch wide strip specimens, with the stripsstill adhered to the glass layer. The 180° peel test is conducted on anInstron™ 5565 under controlled ambient conditions. The initial glassadhesion is tested and the results are reported in Newtons/cm. Threespecimens are tested to get the average initial glass adhesion strengthfor each sample.

The volume resistivity is tested according to the following, which isbased on ASTM D257. The measurement is made using a Keithley 6517 Belectrometer, combined with the Keithley 8009 test fixture. The Keithleymodel 8009 test chamber is located inside the forced air oven and iscapable of operating at elevated temperatures (the maximum temperatureof the oven is 80° C.). The leakage current is directly read from theinstrument and the following equation is used to calculate the volumeresistivity:

$\rho = \frac{V \times A}{I \times t}$

where ρ is the volume resistivity (ohm-cm), V is applied voltage(volts), A is electrode contact area (cm²), I is the leakage current(amps) and t is the average thickness of the sample. To get the averagethickness of the samples, the thickness of each sample is measuredbefore the tests, with five points of the sample measured to get anaverage thickness. The volume resistivity test is conducted at 1000volts at room temperature (RT) and at 60° C. Two compression moldedencapsulant films are tested to get the average.

Materials

The following materials are used to prepare the examples of thisdisclosure.

POE: an ethylene/octene copolymer having a density of 0.880 g/cc (ASTMD782) and a melt index of 18.0 g/10 min (ASTM D1238 at 190° C., 2.16 kg)available from The Dow Chemical Company.

TBEC: tert-butylperoxy 2-ethylhexyl carbonate, an organic peroxideavailable from J&K Scientific Ltd.

VMMS: 3-(trimethoxysilyl)propylmethacrylate, a silane coupling agentavailable from Dow Corning.

TAIC: triallyl isocyanurate, a conventional co-agent available fromFangruida Chemicals Co., Ltd., having the following structure:

TVS: tetravinylsilane, a co-agent available from Sigma-Aldrich havingthe following structure:

TAS: tetraallylsilane, a co-agent available from J&K Scientific Ltd.having the following structure:

Sample Preparation

Soaking:

Compositions are prepared according to the formulations of Table 1,below, by first pre-mixing the organic peroxide, silane coupling agentand co-agent at the desired weight percentages set forth in Table 1 in asealable bottle. The total weight of the organic peroxide, silanecoupling agent, and co-agent for each composition is recorded as X1. Drypellets of POE, depending on the example (see Table 1), are weighed (theweight of the dry pellets for each composition is recorded as X2) andthen put into the bottle for soaking. To ensure a homogenousdistribution and complete soaking of the curing package (i.e., organicperoxide, silane coupling agent and co-agent) into the pellets, thebottle is tumbled for 1 minute and then placed on a roller at roomtemperature (RT) for a certain soaking time (see Table 2). After acertain soaking time (see Table 2), the pellets are taken out from thebottle, and the surface of the pellets are wiped sufficiently usingpaper until no wetness can be found on the used paper. The wiped pelletsare then weighed and recorded as X3. The soaking percentages are thendetermined via the following equation discussed above: (X3−X2)/X1*100%.

Table 2 provides the soaking percentages determined by the aboveequation at certain soaking times for each example at room temperature.Such soaking percentages are also provided in the soaking curve of FIG.2.

TABLE 1 Ex. A Ex. B Ex. 1 Ex. 2 Formulation (wt %) POE 98.75 98.25 98.2598.25 TBEC 1.0 1.0 1.0 1.0 VMMS 0.25 0.25 0.25 0.25 TAIC — 0.5 — — TVS —— 0.5 — TAS — — — 0.5 Total (wt %) 100 100 100 100 Measured PerformanceMH/dNm 1.64 3.18 3.19 2.34 t90/min 14.6 12.1 13.2 14.6 Volume — 2.5*10¹⁷2.6*10¹⁷ 1.8*10¹⁷ resistivity (ohm-cm), RT Volume — 2.8*10¹⁶ 4.2*10¹⁶3.5*10¹⁶ resistivity (ohm-cm), 60° C.

TABLE 2 Soaking time Soaking (min) at RT percentage Ex. B 0 0 60 31.88140 56.96 296 79.54 420 84.63 600 92.91 840 97.49 960 100 Ex. 1 0 0 3070.5 63 88 87 98 110 100 Ex. 2 0 0 32 69.1 71 83 94 93.8 109 95.8 123 97

As seen in Table 2, as well as FIG. 2, compositions comprising aconventional co-agent require a lengthy soaking time for completesoaking of the POE. Such compositions (i.e., Ex. A and Ex. B) arerepresentative of the state of the art. Surprisingly, the soaking time(at room temperature) of TVS or TAS based formulations (with the sameamount of co-agent and the same organic peroxide and silane couplingagent) is much shorter than that of the TAIC based formulations that arerepresentative of the state of the art. Accordingly, it has beendiscovered that replacing a conventional co-agent with a silane compoundof formula (I) (e.g., TVS and TAS) significantly reduces the soakingtime leading to shorter overall process times for forming encapsulantfilms. Beyond this, as seen in Table 1, other important performancefeatures are maintained or improved for the inventive examples, such asvolume resistivity, MH, and t90.

Compression Molding:

Following soaking, the soaked pellets are cured and compression moldedinto 0.5 mm encapsulant films. Compression molding is performed using ahydraulic press. The compositions are pre-heated at 120° C. under noapplied pressure for 5 minutes followed by degassing. Subsequently, thecompositions are pressed for 15 minutes at 10 MPa pressure at atemperature of 150° C. to insure complete curing. Finally, thetemperature is cooled to room temperature and the pressure is released.The cured, compression-molded encapsulant films are then tested forvolume resistivity.

As seen in Table 1, the inventive examples provide similar or comparableperformance compared to TAIC-based compositions (that are representativeof the state of the art) for volume resistivity and curing performance.Accordingly, this disclosure provides novel POE-based compositions thatsignificantly shorten the soaking time of the curing package into POE,while maintaining good curing performance, volume resistivity, etc.

What is claimed is:
 1. A curable composition for forming an encapsulant film, wherein the composition comprises: (a) a polyolefin polymer; (b) an organic peroxide; (c) a silane coupling agent; and (d) a co-agent comprising a silane compound of formula (I):

wherein subscript n is an integer from 0 to 2; each R1 is independently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et and each R2 is independently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et, or R1.
 2. The composition of claim 1 comprising: (a) 80 wt % to 99.88 wt % of the polyolefin polymer; (b) from 0.1 wt % to 5 wt % of the organic peroxide; (c) from 0.01 wt % to 2 wt % of the silane coupling agent; and (d) from 0.01 wt % to 5 wt % of the co-agent comprising the silane compound of formula (I).
 3. The composition of claim 1, wherein the polyolefin polymer is an ethylene/alpha-olefin copolymer comprising a density of from 0.850 g/cc to 0.890 g/cc (ASTM D792) and a melt index of from 1.0 g/10 min to 50.0 g/10 min (ASTM D1238, at 190° C./2.16 kg).
 4. The composition of claim 1, wherein the silane compound of formula (I) is selected from the group consisting of: tetravinylsilane; trivinylmethylsilane; trivinylmethoxysilane; trivinylethoxysilane; tetraallylsilane; triallylmethylsilane; and combinations thereof.
 5. An encapsulant film comprising a crosslinked polymeric composition comprising the reaction product of: (a) a polyolefin polymer; (b) an organic peroxide; (c) a silane coupling agent; and (d) a co-agent comprising a silane compound of formula (I):

wherein subscript n is an integer from 0 to 2; each R1 is independently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et; and each R2 is independently a (C₂-C₄)alkenyl, H, a (C₁-C₆)alkyl, phenyl, O-Me, O-Et, or R1.
 6. The encapsulant film of claim 5 comprising a crosslinked polymeric composition comprising the reaction product of: (a) from 80 wt % to 99.88 wt % of the polyolefin polymer; (b) from 0.1 wt % to 5 wt % of the organic peroxide; (c) from 0.01 wt % to 2 wt % of the silane coupling agent; and (d) from 0.01 wt % to 5 wt % of the co-agent comprising the silane compound of formula (I).
 7. The encapsulant film of claim 5, wherein the polyolefin polymer is an ethylene/alpha-olefin copolymer comprising a density of from 0.850 g/cc to 0.890 g/cc (ASTM D792) and a melt index of from 1.0 g/10 min to 50.0 g/10 min (ASTM D1238, at 190° C./2.16 kg).
 8. The encapsulant film of claim 5, wherein the silane compound of formula (I) is selected from the group consisting of: tetravinylsilane; trivinylmethylsilane; trivinylmethoxysilane; trivinylethoxysilane; tetraallylsilane; triallylmethylsilane; and combinations thereof.
 9. The encapsulant film of claim 5, further comprising a volume resistivity of greater than 1.0*10¹⁴ ohm-cm at room temperature.
 10. The encapsulant film of claim 5, further comprising a volume resistivity of greater than 1.0*10¹⁴ ohm-cm at 60° C.
 11. An electronic device module comprising: an electronic device, a cover sheet, and the encapsulant film of claim
 5. 